The Cell type used within ListView instances. In addition
to the API defined on Cell and IndexedCell, the ListCell is more
tightly bound to a ListView, allowing for better support of editing events,
etc.

A ListView maintains selection, indicating which cell(s) have been selected,
and focus, indicating the current focus owner for any given ListView. For each
property, each ListCell has a boolean reflecting whether this specific cell is
selected or focused. To achieve this, each ListCell has a reference back to
the ListView that it is being used within. Each ListCell belongs to one and
only one ListView.

Note that in the case of virtualized controls like ListView, when a cell
has focus this is not in the same sense as application focus. When a ListCell
has focus it simply represents the fact that the cell will receive keyboard
events in the situation that the owning ListView actually contains focus. Of
course, in the case where a cell has a Node set in the
graphic property, it is completely legal for this
Node to request, and acquire focus as would normally be expected.